Fuel System - Operation and Tests 120 8
IMPORTANT: Remember that all adjustments to the injection pump - except for slow idle - must be carried out on a test bench by a specialist injection pump repair station only. Internal adjustments in the field are not permitted, as this pump is a sealed unit. The Lucas CAV fuel injection pump is a horizontally mounted distributor pump with mechanical governor and automatic hydraulic speed advance. The moving parts of the pump are simultaneously lubricated and cooled by the diesel fuel flowing through the pump; no additional lubricant is required. Diesel fuel for injection is fed to the cylinders by a single unit. The pumping plungers (28) and distributor rotor (24) are fitted with two or four opposed plungers controlled by an internal cam ring (26). On the other end of the rotor, there is a transfer pump (18) which delivers the fuel, drawn from the fuel filter, through the metering valve into the inlet bore in the pump hydraulic head (23), at a pressure which varies with engine speed. As the rotor rotates, the inlet bore in pump head aligns with inlet bore in the rotor. Fuel coming from the transfer pump reaches the pump plunger chamber’s through bore, regulated by the metering valve and forces the plungers apart. During further rotation of the distributor rotor, inlet bore in the pump head is closed and distributor channel in the rotor eventually aligns with one of the outlet bores in the pump head. Meanwhile the pump plungers have reached the cam so that they move towards each other. The trapped, metered fuel is forced, under high pressure, through a channel in the rotor and outlet opening in the pump head. Then, through pressurizing valve and pressure line, to the fuel injection nozzle and into the appropriate cylinder.
A pressurizing valve is located at each outlet in the pump head where the pressure line leading to the fuel injection nozzle is connected. After injection the pressure valve closes again and with its small relief piston, draws in a quantity of fuel from the pressure line. The resulting relief in the pressure line causes a quick and firm closing of the nozzle valve. This prevents fuel from leaking into the combustion chamber. The quantity of fuel which is needed at any given moment for each cylinder and combustion cycle is regulated by a metering valve. The metering valve is controlled by the speed control rod and control lever (11), and by the governor inside the governor housing (8). In the “NO-FUEL” (“OFF”) position, the metering valve completely cuts off the supply of fuel from transfer pump to the rotor. At slow idle speed or under full load, the transfer pump feeds more fuel to the metering valve than is needed for injection. The excessive fuel flows through the pressure regulating valve back to the suction side of the transfer pump. A very small amount of this surplus fuel escapes through the top of the governor housing. To obtain the best possible performance over the entire speed range, the fuel injection pump is fitted with an automatic, hydraulically operated speed advance (25). This speed advance is preset at the factory. The speed advance adjusts timing of the fuel injection pump in relation to engine speed and load. The pump has also a light load advance system which provides additional advance in light load conditions. This system gives to the injection pump about the same beginning of injection as in the full-load conditions. The light load advance is standard on Model DP203 and optional on DP201 pumps. A cold advance switch is optional and aids in cold start-up operation.
CD03523,000011A –19–20FEB01–2/2
CTM125 (22MAR06)
120-8
POWERTECH 2.9 L Diesel Engines 032306
PN=250